Tyre pressures? - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 37 (permalink) Old 07-16-2019, 10:44 AM Thread Starter
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Tyre pressures?

Opinions, please.
I've always run my tyres at 30psi front and 32psi rear, with never a problem.
However, I have just fitted a new pair of K70's and have heard that pressures should be higher for these new tyres. I've carried out a short road test at 32 / 34 and it seemed to ride fine. . .

Any thoughts, gentlemen?



John
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post #2 of 37 (permalink) Old 07-16-2019, 12:23 PM
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interesting ! --- i have alway run with 28 front 32 rear -- cant remember why - its just fixed in head (a very old head) -- i suppose it would make sense to confirm what it should be for current tyres -- alegedly although they are the "old" pattern the compounds are modern so maybe thats the reason
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post #3 of 37 (permalink) Old 07-16-2019, 01:00 PM
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The workshop manual calls for 18/20lbs, front and back. It's pretty well universally agreed that those figures are way too low. Under-inflation of front tire results in bizarre cupped wear patterns.

I've been running 30/32 pounds front and back and that seems to work ok. 32/34 is probably fine - probably just depends on what kind of ride you prefer, what load you're hauling around, and what kind of surfaces you ride on.
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Bruce Miller (hermit47)
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post #4 of 37 (permalink) Old 07-16-2019, 01:04 PM
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Hi John,

Quote:
Originally Posted by suzyfan View Post
have heard that pressures should be higher for these new tyres.
"heard" has confused you. Were you to look in, say, the Owner's Handbook for your bike, it would show 24 psi front, 25 rear; it's those that are too low; modern pressures - even for K70's - are generally 2 bar front, 2.2-2.3 bar rear; so 28-30 psi front, 32 psi rear is

Btw, colours too.

Hth.

Regards,
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Stuart
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post #5 of 37 (permalink) Old 07-16-2019, 02:37 PM
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Hi All, Interesting how the modern K70 wears. In the 70s they lasted much longer front or rear. The front had a propensity to cup the tread off each side of center row & the center not so much.

Now with modern ones the sides of front cup very quickly & the center cups quickly as well. But the sides are much more prone to cupping now that then. I've experimented with tire pressure. As expected the cupping is worse if you run pressures too low.

The rear has always worn in the center, but now it's much worse.

I had no idea of how different the modern k70 was until I got some. With the old spec the tire felt very squirmy, especially on deep rain grooves.

I kept my original tires from when bike was new. The carcass on the modern tire is smaller overall diameter, but mostly similar in width.

I can get about 15k miles on front k70 now until sides are so cupped the handling is very compromised. They get noisy off a straight line in only about 1000 miles.

The rear tire only lasts about 7-9000 miles until center tread is bald. I corner gently, never spin rear wheel & try to avoid skidding. Some get much less miles than I do.

Some don't like the cornering or wet ability of the modern k70, but to me it's better than the originals seemed in the 70s. I've paid attention to how they perform on the club rides. Some guys lean the bikes so far & ride the curves so fast. Keeping up with modern tires. So I don't know what to think.

I like the looks of them so I use them.

I'm 160# ready to ride. I've been running 30 front 31 rear. If 2 up I do 33 rear. I used to run 28 rear, didn't seem to make the center of tire last much longer though. For sure to me the bike handles better with the higher pressure. Odd as it may seem it might ride a little smoother with the higher pressure also. I did some experiments on that. Looking at front tire going over bumps it didn't look like tire was compressing much more with the lower pressure, so not even close to a rim pinch.

I still find the whole tire issue interesting & puzzling.
Don
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post #6 of 37 (permalink) Old 07-16-2019, 05:08 PM Thread Starter
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Thanks for the replies, gents.
As I said, I've run 30 / 32 for donkeys years, so I might just go with that (or a fraction higher).
I have noticed that the bike turns in a lot quicker than with the old Speedmaster / Continental combination. It now seems to respond much better if you drive through the turns with a little more throttle than before.

John
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post #7 of 37 (permalink) Old 07-16-2019, 05:47 PM
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I use 30/32 on my Avon Roadriders. Interesting those K70s have odd wear problems and the Avons just keep in perfect shape. Justifies why i would never fit a K70 again after sliding around on a set with the front wheel stepping out on corners. Regardless of modern compounds, i have never had a worse experience than when i used K70s. TT100 and Roadriders are great tyres. Metzler on the R111 wear badly on the front edge. Avon Cobra on the Thunderbird LT are wearing evenly. I note Don has very good mileage results which are double what i can get on a rear. Might be an indicator that the K70 is a hard compound compared with sticky Roadriders and TT100s which last just under 4000 miles down to the wearbar.

Now,where did that bit fall off ?
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post #8 of 37 (permalink) Old 07-16-2019, 10:46 PM
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Quote:
Originally Posted by StuartMac View Post
Hi John,


"heard" has confused you. Were you to look in, say, the Owner's Handbook for your bike, it would show 24 psi front, 25 rear; it's those that are too low; modern pressures - even for K70's - are generally 2 bar front, 2.2-2.3 bar rear; so 28-30 psi front, 32 psi rear is

Btw, colours too.

Hth.

Regards,
stuart, you and t. e. lawrence are the only people i know of who talk about pressure in atmospheres.

i be kevin
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post #9 of 37 (permalink) Old 07-17-2019, 12:52 AM
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Hi Kevin,

Quote:
Originally Posted by speedrattle View Post
you and t. e. lawrence are the only people i know of who talk about pressure in atmospheres.
Dunno about the US but most European tyre makers' websites quote bar and psi. Using psi, it can look to the casual reader as if there are a large number of differences; however, converting the bar numbers shows most the different psi are actually +/- 1 psi of the bar?

Regards,

Stuart
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post #10 of 37 (permalink) Old 07-17-2019, 02:05 AM
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Tyre pressures should only be described in P.S.I . Anything to do with motorbikes and Bars should be ordering the next Pint at the BAR.
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