What front tire diameter are you going to be using??? Putting smaller diameter tires on will give more positive scrub radius. Increasing the diameter will decrease the scrub radius. Wheel offset will also affect the scrub radius. Small tweaks here can make the difference you need.
I will use the Firestone tiny 4.50 x 16. I calqulated at 26” and wheel is 16” that makes it out 5” radially. ( They is 26.2” tall ) A note ; I will get the Lincoln 1942 brakes on Friday so on Saturday I come back on report... I will also has the tires here this week so I will install them on the wheels. https://www.cokertire.com/tires/450-475-16-firestone-blackwall.html
Don't try to pick the fly shit out of the pepper, if the king pin angle line ends up at the road surface within the tread contact patch the scrub radius is acceptable. IMO of course, others may not agree. And forget about negative scrub radius on a rear wheel drive car, that is for front wheel drive; rear wheel drive should have positive scrub radius as explained previously, stop asking about that.
Not tryna be a dick, and @Blues4U kinda nailed it too, but this still sorta bugs me so... 40 wheel, check. 34 spindle, check. 26.5 tire, check. 40 drums, check. So, those items are gonna be used regardless of brakes? So what changes? The freakin drum lives at 'X' on THAT spindle, no? Yes? I mean this is always good, to do a "...have I got this right?" conversation, but the more revealed here I'm not seeing the major factors changing. 4" dropped 39 axle on mine, 27.5 tires on 60HP 3½ wide 5s. My scrubs are just right, suitable to a head nurse. Ok, kidding but I don't see that short of a massive change in parts anything will change for this. And hey I'm will to get "But you forgot about..." too so there's that. And in advance sorry if this doesn't translate well.
Blues 4U, Again correct. I’m happy what I will see and I’m Ok from positive 1/2” to 2.5” as I simple cant change it anyway. But information is always good to know. Again subject came up when I was into change from the Ford brakes to Lincoln and owner of them - a long time hot rodder told me ; now you get a better scrub ’especially’ since this is the semi offset 1942 Lincolns ( not the 39/40 and not the 41 ) = This got me to look into subject ! ——— Out of topics. I had a thread on Lincoln brakes ( from the Ford 39/40 ) in a late 40’s style build up coupe. I found the Fords more classic and my guess most guy used them back then ( my guess very few did install the Lincoln Bendix or Very few used Kinmount ) I found the Fords more nice look and I’m not really after a little better brakes. So why spend the money ? To get a better ’scrub’ was not either the ’why’. When I look on the Lincoln brakes it look like most Bendix style backing plates up to the 60’s so they look kind of boring. Well maybe drum is more nice. -But what got me to decide this was the ’factor’, and the factor only. I see it as ’if’ a guy after the war rebuilded his prewar coupe and had some money over he invested in speed parts that has came out as Ardun heads and the Halibrand QC. Once there he understand the Bendix brake system was better so he went to the car yard and switched. He did not spend money on chrome and roof was of course chopped since before. Another thing added was allot of S/W gauges. At late 50’s he was beaten by the Chevy guys but never installed a overhead engine but did thought to get a superchager early 1950 but it was never on but he did live with it..
This was the HAMBs odds on favorite from this year's stable of AMBR contestants. Anything familiar to this thread topic? Looks killer! I bet most front shots of the contenders this year would yield the same result. It is hard to get the cool ass wheels and brakes without exceeding that scrub ratio. I know mine didn't make it either, but it drives out pretty damn nice.
Yes I saw that roadster on youtube/pictures. Me, I has understand I’m not a big fan of finned aluminium parts in any form. This one has the big Buick drums so on scrub it will be a huge positive number. But if one like the look thats the way it will be.
This just illustrates how broad the issue is. If I can use an anaolgy, this is like the too skinny tires on too wide of a wheel look employed on many low riders. It's a popular look, but technically it's problematic and has inherant operational problems and potential safety risks. To the owners the look is more important than function, or they don't even know there's a problem with it.
You don't like finned aluminum? That's heretical on a hot rod forum, isn't it? You could be burned at the stake for saying something like that....
I mean it is not my way, but its one of the way hot rods can be builded. I’m more into the factory stamped steel, castings that is painted. Shore polished Halibrand or ex Ardun heads can be nice but I like the cast look. Its the same on louvers, I’m not a fan off that either, can it be nice in special parts - Yes but not to much of it.
I like this super nice shopped 34 3W and it has the 4.50 fronts and I know the owner and he say it goes like a train ( builded in USA )
I mocked up the Lincoln 42/48 brakes that has the semi offset and one can easy see the scrub will be less than the Ford 40 that had maybe +2”. Mock up is ruff and hard see it on picture but its a change from Ford 40.
I'll use a lot harder line then I do most of the time,in hopes,I'll get through too at least a few who need it.; Simple side of things ,bad engineering is not cool and dose not look cool ,except to one who dose not understand. The statement> It dose not drive bad < LOL,,,Is one often used,,but the driver in a lot of cases,,has no idea what bad is,,thinks "Its a old car and should feel the way he feels it"=No he dose not know crap about what he feels{ he puts up with it=feels good too him! }. In his mind,it's all good and been driving it screwed up for years, so it is just fine! Very hard too get across that fools gap,he already knows better between his ears! Real world is,if you stand in front of the car,and most of the brake drum is showing on the inside of the rim /tire,<with 14/15 or even 16in, the scrub is bad an dose act up,with bumps,braking,and turns,also adds to death wabble probs,even if those are damped down by"Putting patchs on too the prob's to cover up{not really fixed,just covered up. up. The real engineering has been layed out a few times in these posts,but still,I read foolish replays,about how some ones car is just fine and dose not follow the engineering. = Too every one that knows how scrub is bad,they see a car with bad scrub and see it as a sign on the car"This is owned by a bit of a fool!" "Wounder what other mistakes it has? None of that adds up to,>I don't like a given rod, often lots of things I like, any that are done with good engineering and smart an ingenious, talented ways. Look for the good also
Dana barlow. I’m happy to get others ideas and not all can be total experts, as a forum its good for what it is and I has a ton of help here. This old cars is far from perfect but one can try understand them and in my case I build the car the old way. I was just going to bought a set of Lincoln brakes ( not because Bendix is better ) but I saw it as a cool thing ( week after I bought them ) The seller told me whit the 42/48 style your scrub will be ’better’ and he drawed it up try to show why. Scrub was going to be ’better’ than on my Ford 40. Thats why I set up this thread. So what is your adwise to me on my set up ? I use Ford 40 4” wheels, 32/34 spindles ( they must be needed to this backing plates ) se picture. This backing plates is the semi offsets as Lincoln has one deeper offset to = 39/40 and this semi offset = 42/48 and the 41 that has the same offset as Ford 40. I can see that on Ford 40 brakes I get around +2” scrub and now on Lincoln 42/48 I get around 1/2”. ( tell me if that is correct ) On pictures I see many has huge positive scrub but the Ford 40 wheels and brakes is very common classic set up.
Maybe I'm looking at the picture wrong; but it looks like the lip of the drum is shy of reaching into the lip of the backing plate. What is keeping it from fitting all the way in?
You are correct, but as I said it was s ruff mount. But it showed the scrub went from + 2” from the Ford 40 to less ( one saw that direct ) Now I removed the dust cap on spindle and calqulsted I needed a ring at 0.15” behind the bearing. Now its from dead backing plate/drum a gap at 0.1” ( maybe ok or I need more clearance )
Dana, I love ya man. You have seen more, done more and know more about these cars than I have time left on this tarmac covered orb to experience. But... I have had friends drive my car (home from the tavern) at speed (too fast) that own well-built hot rods (no RR's) and they can identify no difference between theirs and mine in terms of steering and handling. Yes, I violated the scrub rules when I went with my wheels (but I had to have them) and brakes. I love the bits and I love the way the car performs. Yes, I built a show car number one, but I built a safe car. Again, I aint arguing with you buddy, that would be futile. I am saying though, that my car handles extremely well even when I am out cocking about (often), and I am more than comfortable with it. And therein my friend, lies the "scrub". Maybe if I were a skinny bloke there would be more issue? I keep the front end planted.
When it comes to determining the scrub radius from your pile of parts, you have two constants and one variable. Constants: 1. KPI (king pin inclination) 2. Wheel and tire combination Variable: 1. How far in or out the wheel mounting surface of each of your three hubs is when mounted on the spindle. The brakes will follow the choice of hub. Personally, I would tend toward the 1/2" scrub radius. A +2" scrub radius would put the KPI line very close to the inside edge of the wheel and tire you have chosen. It may be an optical illusion or camera distortion, but in the picture in post 4 it looks like the rod you are using to show KPI has a bow in it.
You really do have a awesome rod Billy ,I love it too. Like said,before! ,You and some others have no idea what they are feeling,and dismiss it.* There for you feel nothing. Your happy in not knowing,thats fine,it dose not change engineering facts. So as long as it dose not do what too much scrub dose,at a bad time. You'll be happy with out knowing the prob. is there anyway,like it or not. I'm always sorry,my bad writing is not good enough to get passed that blockage > "I drive it all the time with no probs",. Should I try again,no not going to help pass what I already have done many times. Just know,I hope your never faced with" I thought I could of stopped in time,or I thought it could turn that corner,that fast." both may of done that little bit better n safe, if less scrub/or same with a few others who are running with bumpsteer,who say they feel nothing=same can be true. I grew up around building both Oval racecars an Sports cars,design ,build an drive. When engineering has been worked out,and proof shown,not to use it,sure has a lot of ways to make up a excuse; So some can cover ,not doing something,after they get away with it as is.. Life is full of "A" to "Q",some don't want to hear. That's why,I don't try to point too poor things I see,all the time,except when asked.. Enjoy the good parts and look for them, even if asked,>well try too be kind,hard to do always though. I really do like anyone who likes rods n customs ,always my type of good n fun,so thank you.
X-cpe. If you look on this picture above I took today on the 42 Lincoln backing plate and see the kingpin. It will go much more into wheel centre and radius 13” out. I will mock up better and has a straigh pin next tine as now I has the 4.50 tires on the wheels.
Dana, ( You might answer in the past, but I’m new into hot rods ) Ok, so if we try to focus ( if you like to help me and maybe others read this thread ) on scrub and not ’people’ that ’can’ make mistakes or even be wrong. But first my, car is build as a old hot rod and I use old parts that been used in the past, and I’m not going circkle track ( I will be use it as a very old guy ) Thread was ; Guy sold this Lincoln 42 semi offset brakes told me it will be a better scrub that my Ford 40 brakes. I’ll just wounder on tech why and what is a ’good’ scrub on this type of cars. I can’t change much ( and will not do ) but say I has a 1/2” scrub - so how about that ? ( I will not get 0 and I will not get +2” ) But exact, I cant say now. -Need mock up better.
3 levels to this shit. On the money, can get away with, and can but really shouldn't. We all see more of the last one than we'd like and sometimes you bite a hole in your lip to remain silent. Sincere questions are always welcome though. Now that the parts above are closer to where they go I'm not seeing too much deviation from optimal.
The EZ way is too say,do it just like the factory!!. Good engineering is the right combo of the best set, of compromised feed back, for max traction an best feel. Worked out by a big team of engineers payed by a factory. But in many cases,we're not using some of the factory parts as made. Some good engineering drawings have been posted,on how to find what scrub your running,as long as you know or can find your sizes. A few drawing are a little miss leading,by not talking about deadcenter of tire patch vs just the edge of tire tread. Too simple it down to basic,{ OK it's not what is called simple really}; The scrub most factory's used for a long time was 4 inch in board of zero< Zero being were kingpin center line runs down an hits the road dead center of tire tread patch. Zero* is not ideal,as some in put from limited amount of scrub, helps to feed balance force from both front tires,plus makes car steer more free,as tire rolls vs twist if it were on dead center { the wider the tread the more twist=even harder to turn.] This on some newer front ends has been cut down some,but not added too ,over the years. So force on spindle from the lever arm* of { the 4inchs or less,can be good for balanced control feed back. But if the scrub is greater ,the feed back can an will get out of hand ,pretty fast as scrub gets bigger{ Shows up as vibration and even darts from bumps an braking ,each of those is a brake in part of tires bite{ so that cuts away part of your front tires traction{ lost of part of control } likely when you need it the most { here is were those that don't feel it,think nothing is going on} Too much scrub, if added to wrong ackermann an bad tow settings,caster/camber, add up to control goes out the window in a turn at a real bad time. You can have a lot of wrong,an rod with feel like it steers super good in a straight line on a smooth road< { let say this fakes you out into being so happy with how it feels} < That's not were a crash is likely ,it's when trying to miss something by turning.
Well I think I need drop this for now. Its hard since I cant say how to even know if test by a straigh pin from kingpin line or scrub radius or the ackerman etc. Its to much factors. If not that is cleared out it impossible try to understand tech. In my car it is what it is anyway. I need my own experiance ( guess its coming ) I’m a dragracer from Mopar muscle and I use Lamb disc brakes and 3.5” Weld forged wheels ( scrub is away from factory my guess ) and I try use allot of caster and camber at zero and some toe in tested jacked up some in a ride height. Never got a issue and cars goes like a arrow ( this Mopar fronts has not the best engineering on planet ) I know rally guys overhere in Sweden so I can ask them but they cant help me on this old car. But shore they can get me tech basics. On my hot rod the parts in front end will be what was used and what I will be used. I will test scrub by use a pin/line from kingpin and down to tire contact to ground. And if inboard tire centre I will call it positive. Right now after read this everything might goes but 0 to + 5” or more sounds how it will be on cars like this. But my question was not that, it was why seller said ; now your scrub will be better.. Ok, I will test ( king pin line test to contact point from tire centre ) and drive it and come back on thread - but it can take some years. Thanks to all try clear this out ( the hot rod way )
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