TR6 15" tires on a TR6 15.5" rim?

[bunzil]

After a bit of research I purchased a set of Falken SN250 A/S 205/70R15 for my TR6. These are to replace an aged set of Kuhmo Solus, same size, that have been on the car too many years. A large sticker is affixed to the new tires saving "DANGER" never mount a 15" size tire on a 15.5" rim, which is what the TR has. Sticker continues to say, "the tire cannot position itself against the rim flange."

This is all news to me. Can anyone comment and help? Thanks.

 

[bunzil]

Never mind my stupid question. I figured it out...all by myself! Duh.

 

[bobhustead]

Never consider trying to mount any tire on a rim made for a smaller diameter. People are killed in the resulting explosions.
Bob

 

[mctriumph]

IMHO the optimal size for most Tr6 drivers is 215/65 15. Better contact patch.Go with a compound
that is soft enough that you have a chance of wearing out the tires before they are old and unsafe.
Mad dog

 

[bunzil]

The question arose because recently arrived 205/70-15's came with a warning not to install a 15" tire on a 15.5" rim and I misinterpreted the 5.5" width of the TR6 rim to mean it was actually 15.5" in dia. Stupid. But what might be of interest to all is my search for a suitable spare as the 205/70 or the 215/65 won't fit well, if at all, in the trunk. Unless someone disagrees, it seems the 165/80-15 is closest to being ideal as it is only .9" and .8" less in diameter than the other two respectively. Plus they are dirt cheap: they can be had on Amazon for around $60. I hope this helps and I didn't waste anyone's time.

 

[mctriumph]

It is worse on a tr3, fitting it into the "cave" seems a 155/70 is as big as you can shove in and expect \
hope to get out later. Good news is that modern tires don't go flat as often as the old bias ply crap
we used to run.
Mad dog

 

[Sarastro]

I have 195/65R15 tires on the car, with 6" wheels. For a spare, I just got the same tire in a narrower width and mounted it on an original disk wheel. It fits into the spare-tire well just fine. Driving on mismatched tires is, of course, not a good thing to do, but I think it is OK in a "limp home" mode, much like those compact spares in modern cars.

Also, I take advantage of the Law of the Inherent Perversity of Life: if I don't carry a spare, I'll get a flat almost immediately, but if I do, I'll never get one. So, the spare really exists to protect my other tires.

 

[Gliderman8]

I have a donut from an Acura as a spare. The bolt pattern was identical and it of course fits in the trunk of my TR6.

 

[mctriumph]

The bolt pattern is identical???? I believe they are close but no cigar. 4x100mm is not the same as Triumph.
You might bang up your studs......
Mad dog

 

[Tybalt]

First, let's talk the standard TR6 configuration, the TR6 for the North American market was fitted with 185-15 tires and while not listed, at that time the majority of tires were an 80 aspect ratio. If they were different, the aspect ratio was called out in the tire size marking.

My take from personal experience is that in general I think the upper limit is a 195 section width with a 70 aspect ratio on a 5.5" wide wheel. I did run some DOT street legal 205/50-15 tires (with a tread wear rating of 40, not a typo, it was really 40) on stock TR6 wheels when I autocrossed that car in what was then the SCCA E Stock class but felt it was very doable at that extra width because the sidewalls on those tires were stiff and the aspect ratio was smaller. For street use, I ran 195/70 x 15 tires on 15 x 5.5 or on 15 x 6 wheels depending on when we are talking about in my ownership of that car. Compared to the stock tire size, this resulted in a speedo/odomter error of ~ 3% percent. I tried a 205/70-15 but wasn't particularly happy with it. While that 205/70 x 15 can be done on stock 5.5" wide wheels it seemed be a bit more flexible and there was a loss "feel" because of the slightly higher sidewall and the greater bit of curvature in that sidewall when mounted and driven under load when pushed. With that size tire, I calculating a speedo/odometer error of ~ 1.3%. I knew plenty of people that had run that size on their TR6 and it seemed to work for them but don't really know how hard they exercised their cars.

Jumping up to the 215/65, I wouldn't even think about that on 5.5" wide wheel, at that point I think you need to be thinking in terms of 6.5" wide or 7" wide. With that size, the speedo/odometer error crunchs out to ~ 2.5%. I did know some people that used wider wheels and ran that size tire. Some had tire interference problems with the front fender, some did not. It was probably tied to the offset in whatever wheel they used but know nothing definitive on that.

Regarding lug pattern on the TR vs Acura, it depends on the Acura model in question. The Civic based four lug pattern is too small at 4 x 100, same as Saturns, many Hyundais/Kias, Mazdas, etc. The larger four lug patern Acuras use a 4 x 113/4 x 4.5, same as many four lug Fords, many Mazdas, Nissans/Datsuns, etc along with many LBCs.

 

[glemon]

IMHO the optimal size for most Tr6 drivers is 215/65 15. Better contact patch.Go with a compound
that is soft enough that you have a chance of wearing out the tires before they are old and unsafe.
Mad dog

Although I am asking the question too late (I just ordered a set of 205/50-15 autocross tires for my TR250) does a 215 or 225 Section width fit on a stock TR250/6 without rubbing?, I suppose the sidewall height might matter too). Thanks for any information.

 

[Tybalt]

Although I am asking the question too late (I just ordered a set of 205/50-15 autocross tires for my TR250) does a 215 or 225 Section width fit on a stock TR250/6 without rubbing?, I suppose the sidewall height might matter too). Thanks for any information.

Above I did mention what I had seen with others running a 215/65-15. Some had interference issues at the front, others did not. I never really dug into it but since they were running wider wheels, it could have been tied to the offset of those wider wheels and/or the springs they were using.

You don't mention what aspect ratio you are thinking of in terms of the 215 or 225 section widths or which class and sanctioning body autocross rules would apply. Operating under the assumption that it is SCCA Solo II rules, there are limits on the wheels that could cause you problems in the "E Street." You can use a different diameter wheel than stock, but not a different width wheel from stock plus the offset of any other than stock wheel must be within ±7 mm/0.275" of the stock wheel. Since the TR250 came with 4.5" width wheels, the 205/50-15 is well over the maximum section width tire I would recommend for a 4.5" wide wheel. As for a 215/50-15 or a 225/50 or /45/40-15, I would go straight to a 7" wide wheel and with the low aspect ration clearance should not be an issue provided that you have a reasonable wheel offset.

Two additional categories are "Street Touring" and "Street Prepared." I like the concept of Street Touring in that it allows a nice variety of bolt on modifications that are popular but outside the bounds of what is permitted in the "Street" classes. It keeps the requirement to run a tire with a minimum tread wear rating of 200 from the street category but allows wider wheels. Unfortunately they do not have any Triumphs classified in any of the various Street Touring classes. Off hand I would have to say that it would fall into either Street Touring Roadster (STR) or Street Touring Sport (STS). I'm leaning toward STS since it has a "catch all" classification that would cover a TR250 or TR6 while there is not a "catch all" classification in STR. In STS the maximum wheel width allowed is 7.5" and the maximum tire section width allowed is 225. Those numbers are 9" wide wheel and 255 tire section width in STR.

Then for "Street Prepared" the six cylinder Triumphs fall into "F Street Prepared." If you plan on using the car as a street car as well as an autocrosser, I would not recommend this class. When I was autocrossing a TR6, the Street Touring classes did not exist so the jump was from "E Stock" to what was then "D Street Prepared" with the TR6. In order to make the car competitive in DSP, it became a lousy street car. Prep rules are kind of convoluted since it is basically a class somewhere in that middle ground of the "Street' classes and the "Prepared" classes. As far as wheels and tires go it is almost jungle rules territory. Regarding wheels, it's pretty much a matter that if you can fit it you can run it. For tires, the only stipulation is that the tires be DOT approved, this is where you can find yourself looking at tires with tread wear ratings of 40..

 

[Tybalt]

Something I thought about and then failed to mention was triggered by something seen in the latest issue of Grassroots Motorsports that hit the mailbox today. In it, one of the comments printed from their message board was "Tire companies have rubber rulers." I can't speak to the materials used for their rulers but can say that they must not all be using the same rulers even between different tires within the same brand. You really need to look at the detailed information on that particular tire from the manufacturer for sizing information. I had put together a spreadsheet to compare different tire options for two cars that both needed tires at the same time a few years ago.

One size was 215/45-17 on a 7" wide wheel. While the diameters were consistent across that table, there was a top to bottom variance of 0.1" difference in section width and 0.6" difference in tread width. Weights ranged from 21 to 25 pounds. I'll pick on Bridgestone for a second here, three tires in the comparison out of seven tires total and tread widths were 7.4", 7.7' and 8.0" while weights were 22, 24 and 25 pounds.

In the 225/40-18 tires on a 8" wide wheel, diameters showed a 0.1" difference across the comparison, section width difference top to bottom was again 0.1" but this time the tread width difference was 1.0" (7.7" to 8.7"). Weights were from 22 pounds to 25 pounds.

 

[glemon]

Tybalt, thanks for the info. I don't run in SCCA, it is our local British car club and very much a "formula libre" situation. My goal with the TR250 was always to make it perform better without making it awful to drive on the street. I have Addco front and rear sway bars, Koni shocks, Nissan R200 diff, lowered about an inch front and rear, stock springs, 7" x 15" Konig rewind wheels.

The new tires I got are 205/50s. They will be autocross use only as they are marginal street tires and my ground clearance with the new tires will be pretty low.

Most everybody competitive is running 200TW tires the last few years, lot of Miatas in the mix too.