New Tires for a TR6

For the past several months I have been pondering the purchase of new tires for my Triumph TR6. While this shouldn’t be a big deal, there were several considerations I had to bear in mind before making a decision. I sought the advice of experts and read several articles on the subject. Some of the advice I picked up may be of interest to anyone else looking for replacement tires for their British sports car.

Originally all US-bound TR6s came equipped with 185R15 size tires (Redline Michelins or Goodyears). These are 70 or 80 series profile tires, which is to say that the sidewalls are roughly 80% as high as the tire is wide. They look very good on the TR6 and provide a smooth, compliant ride. Being so tall and narrow these tires offer little as a performance tire. In addition, new 185R15s can cost upwards of $200.00 per tire— if you can find them!

A popular replacement for the 185R15 is a 205/70R15 size tire. These are readily available and will fit the 5.5” rim original to the TR6. The 205/70 tire has an overall diameter of 26.3” so in comparison to the 185R15s the tire diameter is virtually unchanged from the original’s 26.6”. This means that speedometer and odometer readings should not change, an important consideration.

Another important consideration is how the car will be used. Back in 1987 when I was using the TR6 daily, I purchased a set of used 195/75R15 tires to get me around town. Like 205/70R15s, they are almost equal on overall diameter to the original tires, but as I started to use the 6 as a weekend cruiser and occasional autocrosser, cornering performance became more and more of a consideration.

As I began my search for new tires I also had to be aware of how they would affect the overall ground clearance, gearing and aesthetics of the TR. Fifty profile tires would be the ultimate cornering tires, but weekend driving would be hazardous as speed bumps, driveways and potholes would become damaging hazards. Fifty profile tires would also radically alter the final gear ratio of the car making highway cruising difficult. On the other hand, acceleration would be greatly improved.

The compromise I chose between performance and the other considerations was to go with 205/65R15 size tires. The overall diameter of these tires is 25.5” about 1” shorter than stock. Ground clearance is not a problem and the tires appropriately fill-out the wheel wells for an updated, but not bad look.

As far as driveability, the overall gear ratio did change slightly. To figure out the new overall gear ratios and speedometer readings I used the following formula found in Grassroots Motorsport.

To find my new highway speed at 3500 rpm, the formula is: overall tire diameter times engine rpm divided by the differential gear ratio times selected gear ratio times 346.

So, at 3500 rpm in fourth gear (no overdrive on my car) my speed is (25.5 X 3500) divided by (3.71 X 1.0 X 346) = 69.52 mph. My old speed at 3500 rpm was 72 mph or thereabouts. So as far as driveability on the road there is not a great deal of difference with my new tire choice.

There is a great deal of difference out on the autocross course however! The tires I chose are made from a softer compound and carry a “V” speed rating. Even though 65 profile is still on the high side, they’ve made a great improvement in handling over my old high-mileage ‘truck’ tires. The car is now much more responsive than before, quicker, and so much more fun to drive.

The trade-off for the improved performance has been a harsher ride. The old 195/75R15s were very forgiving of minor bumps and road irregularities. Though lowering the tire pressures has helped somewhat, the new tires will never be as ‘cushy’ as the old ones, but this is a compromise I can learn to live with because of how I wish to use the car.

If you’re considering the purchase of new tires for your British classic I hope my experience can be of some use to you. The best advice I can offer is to talk to a qualified tire technician who will listen to what your specific needs are and recommend accordingly.

By Kevin D. O’Connor


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'New Tires for a TR6' have 5 comments

  1. June 14, 2013 @ 9:24 am mike

    Thanks for the info. I’m currently looking for tires to fit to 15×5.5 Panasport wheels…All the purist say 195/65, but I’m thinking 205/65 will be better. I’m hoping I won’t find any fitment problems with these sized tires/wheels on a 4A. Thanks again

    Reply

  2. May 20, 2016 @ 8:51 am Stephen Bardon

    Mike,
    Thank you for the insight on tires, I have a 1976 TR6 CF51884U, it has 85,000 miles on it, all original as are the original Michelin X Redlines.
    I am running tubes and have recently inspected the tires and there is still good tread (although hard) and not a single crack anywhere.
    Having said that, I understand the safety concerns of the old tires and am looking to replace them.
    In reading all I can about replacement tires, there is one aspect that seems to be missing from everyone’s comments, an aspect that I have found over the years to be the most relevant, tire pressure.
    I am pretty good at reading the manual, and both the manual and the placard inside the glove box call for 20 psi front and 24 psi rear. I run about 22 Front / 26 rear and have found this to be the best combination of ride and match to the suspension for handling. I have tried a range higher pressures over the years and find that the ride deteriorates dramatically and that the cars ‘grip’ becomes unbalanced over these factory specs.
    To be honest I would love to buy some new Michelin X Redlines, run tubes, and continue to enjoy the classic ride. yes I do some occasional spirited driving, but mostly cruise, as per the original tires lasting this long.
    Any idea of what tire would best emulate the Michelin X and be able to be run at the lower tire pressures (22F/26R, probably requiring a tube)?
    My heart is set on redlines… but I think I would choose the ride over the look. Even though I love the redlines and think they are a significant part of the cars look. BTW mine is Pimento, black interior, roll bar, overdrive.
    Your input would be greatly appreciated.
    Regards,
    Stephen

    Reply

  3. September 14, 2020 @ 9:35 am Drew

    I need to purchase front tires for my 1975 TR-6. The guy before me put 185/ 70/ R15 on the front and 205/ 70/ R15 on the rears. I would like to put the 205/ 70/ R 15 on the fronts, but am concerned the tires might be too large and rub on the wheel wells.

    Is the 205/ 70/ R-15 an appropriate size for the front of the TR-6?

    thank you,
    drew

    Reply

    • April 15, 2021 @ 8:11 am David Militello

      I have 205 70 15’s all around my 75 TR6 and have no problems with rubbing or clearance.

      Reply

  4. September 16, 2020 @ 6:08 pm Paul Goodwin

    Well ; I just bought the Konig rewind wheels from Moss for my TR6 and can’t find out what tyres I need. 15″ x 7″ now as original stock wheels at 15″ x 5.5″ Anyone have a recommendation for the correct high performance tyres I need to get ?

    Reply


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