Technical > Jon's Wheel House

Rim width V's tyre size

(1/1)

retroboy:
Howdy
I see mention here of running 10.5 tyres on 12 and 14" rims. I ran them on 8 and 10" rims back in the old days. What's the pros and cons of various combinations?
Cheers

JrFuel Hayden:
When was your "back in the old days" ?  I thought the 10.5 tires are kinda new and built for the 10.5 door car classes.  When I raced my Nitro Jrfueler we ran 8" or 9" wide tires and rims in 1963-69, with smoking the tires for about half track, way different tires and tracks we have now. M/T 10.5 tires are designed to run 13-14" wide rims, to get more tread width. Keep in mind 10.5 tires are designed for 2500-3000+ lb door cars not for 1300-1600 FED. Now with that in mind my friend Craig Bourgeois won the 2015 Comp Elim championship with his B/ND [JF] FED running 29x10.5x15 MT on 12" wide wheels [ rules limit]. Criag ran some .987 sixty foot times, with his 4.88 gear and that short 29" tire, but keep in mind racing in Comp most of the time you don't run it 1320' [ finish line racing]. When he did run it closer to the finish line , he was at 10,600 rpm.
Craig likes the stiffer side walls , again 10.5 made for heavier door cars, so he has less tire shake. His 10.5 is a 10.5 "S" I think for stiff, and MT also makes a 10.5"W" for wide, like 11" wide tread.
I have tested some 33x10.5Wx15 with a 5.14 gear, and don't shake, but I still ran better ET's with the 31x12x15 Goodyear. I plan on testing more at the Div 7 race in Sonoma. The plan is to try different tire pressures , last time testing was at 7lbs, different launch RPM, and maybe a different converter.
We mostly just race the NHRA Heritage series with limited Q runs [ 1-2] but we get at least 4-5 runs , icluding at least E-1, at the Div 7 race. 
Again MT recomends at least 13" rims on the 10.5 tires, and I ran them on my 12" rims because of the JF , and B/ND rim limits.
I hope this helps ,
Jon

noslin:
my understanding why the door car guys run the 10.5 on wider rim is so the sidewall wont wrap as if it would on conventional mounting situations +/- 1" of rim width normally (correct?).  some of those guys will run the 10.5 on a 15" wide wheel.  the 8.5 tire guys will use 12" wide wheels. 

i know some A/F are running the 'big bubba' or something like that. its a ??x10.5x16 tire. 

raises the question and i guess its all in how a person feels like setting thier car up but what would be optimal.  sense the FED dont have shocks, is the tire considered partly a shock?  meaning, on a live axle door car the shocks are used for tunning where as in FED there isnt that luxury.   

so, if you make the tire stiffer, what changes or affect does that have on setup assuming the conventional setup with +/- 1" rim width to tire premise.  thinking about it, if stiffer sidewall i can see the tires ability to get up on the tire would be quicker since that energy isnt wrapped up in the tire waiting for it to un-wrinkle.  i could see downside to this is smaller window to getting wheel hop/tires spin.  and flip side would be with conventional setup if not enough power would be criticle as well with not having enough power for bigger tire and getting wheel hop.

ty
dean

retroboy:
I ran 28.5 x 10.5 M&H Racemasters on an 8" rim 35 years ago then went to a Firestone (?) 28.5 x 10.5 on a 10" rim which were a big improvement over the M&H. I currently have a 31 x 13 wide M/T tyre on a 10" rim and when they're worn out I was thinking of going to a 10.5 M/T on a 9" rim.
So the use of a wider rim is to effectively reduce reaction time of the tyre wall ? and or mandated by various rules? Yes?
Cheers

JrFuel Hayden:
Mr Retro your 10.5 tires that you ran 35 years ago, is not the M/T 10.5 of now. It may be that going from your 13" tires to the M/T 10.5 may get you too much bite and it could bring your RPM down below your good HP range.
 I believe M/T designed that tire to run in the 10.5 classes. The idea, was to limit the tires to 10.5 to reduce the cost of racing, less tire = less HP needed. However M/T figured out by running a stiff sidewall tire on 13" wide rims they would work like the 14-15 wide tires the door cars used to run.
So I think you should call M/T to give them your combo, and goal to get their suggestion on rim size and tire pressure. Again, a 3000 lb door car with rear ladder bars is not a FED.
The fast Heritage A/F guys started trying the N/TF tires [ 12" limit] to hopefully get rid of tire shake. K. Bates had so much tire shake it would really shake the fillings out of his mouth. The TopFuel tires had stiffer sidewalls because of the 12" rule  limit.   I think Craig tried the 29" 10.5 tire because he has a 12 bolt drop-out rear end, and there are fewer gear choices than 9" Ford, he was looking for something between the 12 bolt gear choices. And he was used to racing the GY 31x12x15 tires that were made in Chili, which have not been made in over 10 years, so I thought it is clever to try the short M/T's.
Another thing about the A/F cars is up until just recently the rules limited the rim width to 15" , so one team paid big bucks to make a set of 15"x16 wheels, because there are lots of 16x16 rims but uncommon are the 15x16 wheels . Well they just got a rule change to 16x16 rims, which is what M/T suggested with those tires.  BTW there are 2 A/F teams that have run in the 5's.
Craig is the only JrFuel type car that I know of that is very sucessfull at running the 10.5 M/T tires. Other have and are trying, but Craig is hauling A__. One thing about his great 60' times are I built him a set of 21" wire wheels and tires about 5 years ago. Because Comp uses a .5 Full tree, he can leave earlier than the bottom yellow. Heritage is only .4 Pro Tree, so no advantage to run 27.5" tires unless you have a RedLight problem. 21" wheels give a FED a 4" head start on the lights compared to 17", besides the 21's steer better.   
Feel free to call with any questions, 800-624-3803
Jon

Navigation

[0] Message Index