What size wheels should I run 13's or 15's

Anyone have experience with running 13's with a 3.88 FD?

My lack of experience with air cooled engines is apparent in my overall drive ratio. With watercooled VW's you can run them all day long a 6000 RPM if you want and suffer nothing but hearing loss. With these air cooled engines I am a bit nervous and want to make this engine last. Mainly the car will be in town or within 50 miles of home. But the ocassional road trip of up to 300 miles (one way) would be nice. The engine is a 1955 with dual 44 IDF's


I mapped out the speed difference vs RPM and have the following:

215/50R13 or 205/50R15
2500 47 MPH 50.3 MPH
3000 56.5 60.4
3500 65.9 70.4
4000 75.3 80.5
4500 84.4 90.6
5000 94.1 100.6
5500 103.5 110.6
6000 112.9 120.8

Definately 15s. and IM. uses 185 65 15s front and 195 65 15s rear in the Dunlap brand If you want to rotate them go with the 185s' All around

If your car is a C body with the flared fenders 205s might work but I have little experiance with the C cabs.. You are right to be concerned the heads will heat at higher speeds under a full load. A BAD BAD THING!

If the engine is stroked between 74 and 84 even more important to keep the rpm's low less you sling a rod.. a 26 inch tall tire is better in that case but hard to fit on these cars.

Forgot to mention the car is a flared CMC body which was designed to run 15x7 wheels and 3.75 of backspace. Note the difference at freeway speeds (75mph) is 250 RPM.

I think that 13 in rims would rule out disc brakes, if you were considering them.

Boston Bob E

A flared body with 13" wheels...
Yep, make a good-lookin' golf cart.;)

Being your car Is a C body start with fitting the front making sure they don't rub from right to left as you work the steering . They tend to rub the ball joint arms. when the backspacing is to close . Watch for that. The back spacing on the rear trailing arms will be the issue on the back.

I'm sure someone here can suggest a good rim fitment.

We were all thinking it, but Barry was the only one to say it - DIAMETER is what controls the RPM, not wheel size. You can probably run near any wheel size, from 13 inch up to 18 inch, if you select the right tire size for the RPM you want.

Yes, you will suffer brake issues using smaller wheels. Yes, you will suffer tire width issues for body clearance using larger wheels.

Like Jake says regarding engines, but applicable to many other applications, "It's the total combination".

Then the opposite side of the argument involves weight...

The less rotational and unsprung weight you have (aka - wheels/tires!) the better your car will accelerate, brake and handle.

In that area, a 13" wheel with a light tire will excel (overall diameter small) will be the best choice. I think I once heard an estimate that every bit you take off of your wheel/tire combo is equal to 3 times that number when it rotates. So losing 5 or 6 pounds on the package is equal to losing 15-18 pounds at each corner when you are moving...

Adds up fast. Choose your overall diameter for rpm on the highway, but within that diameter, the lightest wheel/tire package that will fit is going to be your best choice. Not an easy choice - LOL - but the best choice!

angela

Good feedback. I used the tire rack data for the Speed vs RPM calc. The 13's (I would run 215/50/13) are 21.6 in dia and weigh 19 lbs (rubber only)

The 15's are 23.1 dia and weighs 21 lbs rubber only.

Mainly I have seen Manx buggies at autocrosses in my area top three times in the day using 5.5 inch wide 13 inch wheels with formula vee cantilever slicks.

I would like the speedster to handle really well since it is going to be relativley underpowered.

If your vehicle has less power, then you have to make the absolutely most of it by keeping your unsprung weight down. You have already identified 2 pounds per tire for a 13 versus a 15. Now about the rims...

This is a chart for Fuchs wheels. There are no 13's on it, but I'm just trying to give you an idea of weight differences for wheel size.

http://members.rennlist.com/911pcars/WheelWts.html

Compare the 7x15 fuch to the 7x16 fuch. Twelve versus 18 pounds. Six pounds!!!! Same maker, same width, both forged wheels... SIX FREAKIN POUNDS!!!! This varies by maker, but the point is, that taller wheels, even in the same width can be much heavier.

Shop with care. Consider your wheels and tires to be a package that is an integral part of the vehicles performance. And if you can, find an old set of Mahle gas burners (9 pounds) - LOL!

angela

Good to know. I am very interested keeping this car sporty since it will be a while before I end up building the sports car of my dreams (locost Hayabusa). Now I will have to weigh that with the asthetics of the 13's

Sounds like nonone has run 13's here so off to post on the Samba to see if anyone has ran them on a bug. Mainly I want to make sure they clear the brakes steering.