[Arizoni]

I just finished reading the book, "BSA TWINS & TRIPLES, The Postwar A7/A10, A50/65 and Rocket III" by Roy Bacon and noticed something I think is interesting.

As many of us have found,  Royal Enfield recommends very low tire pressures on our bikes. 
For instance, my UCE G5 Owners Manual says the front tire should be 18 psi front and 28 psi rear for solo riding and 20 psi front/30 psi rear for dual.  It lists the G5 wet weight as 187 Kg (412 lbs)  I should note that the weight of our gasoline + oil is about 35 pounds so the dry weight would be around 376 lbs.

The high tire pressures common on many modern motorcycles (and that I found on my new G5 as delivered from the factory) can cause our RE's to not only ride hard but to get skitterish to the point of causing some disgusting surprises in our shorts,  at higher speeds.

In the back of the book, a number of specifications are listed for all of the BSA twins and I noticed that the tire sizes and pressures were given as well as dry weights.

The A7 (500 cc, 1946-1954) used a 3.25 X 19 front tyre and a 3.50 X 19 rear.
Recommended tyre pressure: 16-18 front, 17-20 rear (solo) and 18 front, 26-28 rear (dual). Dry weight about 382 lbs.

The A10 (650 cc, 1950-1961) used a 3.25 X 19 front and a 3.50 X 19 rear tyre.
Recommended tyre pressure: 18 psi front, 20 psi rear (solo) and 18 psi front, 28 psi rear (dual).  Dry weight about 408 lbs.

The A50 and A50C (500 cc, 1962-1970) used a 3.25 X 18 (A50) or 3.25 X 19 (A50C) front  and a 3.50 X 18 (A 50) or 3.50 X 19 (A50C) rear tyre.
Recommend tyre pressure: 18 psi front, 20 psi rear (solo). Dry weight 385 lbs.

It seems the tire sizes used are the same as our Royal Enfields and the weights of the bikes were very similar so it's not  surprising that the recommended tire pressures for our RE's are so low.

I've heard some people say the RE's recommendations for tire pressures are so low they might be dangerous, possibly allowing the tires to slip on the rims but it seems the low pressures were common on the old bikes and I don't recall that things like that ever happened.

Maybe some of the historical information is as valuable today as it was back then.  Especially when riding a bike that is the same today as they were in the 1950's. 

[Vince]

     Obviously, you should run the tire pressure that works best for you. Keep in  mind the era in which these specifications were formulated. Frame geometry was different than modern bikes. Roads were rougher. Suspension was substandard by today's standards. Tire manufacturing methods and materials were different. Low pressures helped compensate for all these conditions.
     Modern Enfield suspension is not a whole bunch better than it was 50 years ago. Steering and frame geometry are not much changed. In India, particularly, and in modern cities the roads are often not very good. So a good case can be made to run tire pressures on Enfields that I would consider to be dangerous on a more modern bike.
     A lot of us here also have more modern bikes to go along with our Enfields. I encourage everyone to consider the differences from then to now when setting pressures in modern bikes.

[barenekd]

Are you calling an Enfield a modern bike? Are are you telling us not to run low pressures in a Yamazuki Kwakahon?
If you are thinking about putting a lot of air in your Bullet, I would suggest ATTGATT and a pair of Depends before you get very froggy with it!
Bare

[Arizoni]

Well, I didn't intend to imply that anyone should run low air pressures in their Hondyamazuki.

Modern bikes with modern tires like a Hondyamazuki should use the tire pressures that the maker suggests.  Maybe even higher than the maker suggests if the bike doesn't show any bad traits (like tank slapping).

That said, I think it is somewhat comforting to know that the Royal Enfield is carrying on the tradition with spoke wheels and with low pressure tires just like those of the 1950's. 

[Kevin Mahoney]

The biggest reason for low tyre pressure recommendations especially on the C5 models come from the tyre/bike combination. The tyres that come with the bike have a very stiff sidewall, much stiffer than the Speedmasters on the regular Bullet.

[Anon]

I guess it's a case of whatever works for your bike and tires, but if I want to scare the crap out of myself and feel like I'm driving on wheels that area bout to come off, low tire pressure will do it in a flash.  My bike ('06 iron barrel) feels WRONG if the front tire gets in the low twenties.  It feels right at about 28-30 psi and gets progressively worse the lower you go.  I've never been brave enough to go lower.  My back tire feels best at about 30-32 psi, and too much lower than that I feel like I'm fishtailing.

This is with Avon AM26 Roadriders, sized 90/90-19 and 100/90-19 respectively, although I had similar results with the stock 19" Speedmaster/Safety Mileage combo.  The low tire pressure thing that is obviously something that works for some of you guys, but it's not like the rest of us just haven't tried it and would be so much better off if we just did. 

[r80rt]

The biggest reason for low tyre pressure recommendations especially on the C5 models come from the tyre/bike combination. The tyres that come with the bike have a very stiff sidewall, much stiffer than the Speedmasters on the regular Bullet.

Yeah, the low pressure is a C5 with stock tires thang.

[olhogrider]

Yeah, the low pressure is a C5 with stock tires thang.

+1 to what they said. Low pressure really transforms the C5. I had been running the shocks at full soft to compensate for the hard tires. I felt the occasional jolt up the spine. The I thought, since the tires are now absorbing some of the shock I should try some preload. I went full stiff. Probably too much, but no more jolts. Another big improvement!

[boggy]

I run around 22 front / 24 rear on my '07 AVL.  Stock Avons.  I ride pretty fast, and fairly aggressive compared to expected-Bullet-behavior.  I'm guilty of doing my best Valentino Rossi impression around corners and put my knee down as far as I can.  I've never felt unstable or squirrely on my Bullet.  Scooter Bob (if I remember correctly) recommended that pressure and it works "for me."

Only thing that's made me go white-knuckled is good side wind.

[single]

I am running 30frt 32rr.Front is K70,rr is stock original. Lotta cracks in it.These pressures and the Dunlop on the front have turned the rain grooves into a non event.With the stock tires the lower the pressure the better,in my experience.I have not seen any real difference in cornering but believe it is better.I do not push it hard in corners as I am rarely able to see very far around them and with all the agricultural activity I am fearful of machinery in the road.Or,maybe just fearful.

[barenekd]

It lists the G5 wet weight as 187 Kg (412 lbs)  I should note that the weight of our gasoline + oil is about 35 pounds so the dry weight would be around 376 lbs

The fuel/oil weight is more like 25 lbs. 6 lb/gal for gas, 7.5 lb/gal for oil. Put us at 386, give or take a few. I think they also specify 90% capacity. Not to be picky though, It's mostly irrelevant seeings that most guys have done a few lightening exercises to their Bullets.
I  don't want anyone to think I'm doing a personal attack on anyone.
Bare

[ROVERMAN]

Got to agree with eamon on the iron barrel tire pressures.I use 28 fr, 30-32 rear,anything less and it gets ponderous and squirrly, fast,-stock Avons with 2500 mi.